Devices for hydrogen production and methods of fabricating a hydrogen catalyst layer

ABSTRACT

Disclosed herein are devices for hydrogen production and methods of fabricating hydrogen catalyst layers. The method may comprise forming on a substrate a first horizontal crystal and a first standing crystal that include each molybdenum oxide; forming a second horizontal crystal, a second standing crystal, and a preliminary layer on the second horizontal and standing crystals by supplying a sulfur gas onto the first horizontal crystal and the first standing crystal, the preliminary layer including molybdenum disulfide (MoS 2 ); and removing the second horizontal crystal and the second standing crystal.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. nonprovisional application claims priority under 35 U.S.C § 119 to Korean Patent Application No. 10-2018-0173442 filed on Dec. 31, 2018 in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.

FIELD

The present inventive concepts generally relate to a device for hydrogen production and a method of fabricating a hydrogen catalyst layer. More particularly, the present inventive concepts relate to a device for hydrogen production including molybdenum disulfide and a method of fabricating a hydrogen catalyst layer including molybdenum disulfide.

BACKGROUND

Hydrogen is known as a future eco-friendly energy resource. At present, hydrogen is mostly generated by a chemical byproduct hydrogen production method in which toxic byproducts are formed. Eco-friendly water electrolysis using platinum exhibits a high efficiency of hydrogen production, but has disadvantages in that expensive platinum must be used. Recently, due to its relatively low price resulting from rich reserves and its high efficiency in hydrogen production, molybdenum disulfide (MoS₂) has been actively studied as a catalyst used for eco-friendly water electrolysis for hydrogen production.

SUMMARY

Some example embodiments of the present inventive concepts provide a device for hydrogen production with high efficiency.

According to some example embodiments of the present inventive concepts, a method of fabricating a hydrogen catalyst layer may comprise: providing a substrate comprising a first horizontal crystal and a first standing crystal that each include molybdenum oxide; forming a second horizontal crystal, a second standing crystal, and a preliminary layer by supplying a sulfur gas onto the first horizontal crystal and the first standing crystal, wherein the preliminary layer is on the second horizontal and second standing crystals and includes molybdenum disulfide (MoS₂); and removing the second horizontal crystal and the second standing crystal.

According to some example embodiments of the present inventive concepts, a method of fabricating a hydrogen catalyst layer may comprise: forming on a substrate a first horizontal crystal and a first standing crystal that each include molybdenum dioxide (MoO₂); forming a preliminary layer on the first horizontal crystal and the first standing crystal; and removing the first horizontal crystal and the first standing crystal. The preliminary layer may include molybdenum disulfide (MoS₂).

According to some example embodiments of the present inventive concepts, a device for hydrogen production may comprise: a substrate; a horizontal structure that lies on the substrate and extends in a first direction that is parallel to a top surface of the substrate; and a first standing structure and a second standing structure that extend in a second direction that intersects the top surface of the substrate. Each of the first and second standing structures may include: a first standing segment and a second standing segment that are parallel to each other; and a first void between the first standing segment and the second standing segment. Extending directions of the first and second standing structures may cross each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view showing a device for hydrogen production according to some example embodiments of the present inventive concepts.

FIG. 2A illustrates a cross-sectional view showing a device for hydrogen production according to some example embodiments of the present inventive concepts.

FIG. 2B illustrates an enlarged view showing section A of FIG. 2A.

FIGS. 3A, 4A, 5A, and 6 illustrate schematic diagrams showing a method of fabricating a hydrogen catalyst layer according to some example embodiments of the present inventive concepts.

FIGS. 3B, 4B, and 5B illustrate enlarged views showing section A of FIGS. 3A, 4A, and 5A, respectively.

FIGS. 7 and 8 illustrate schematic diagrams showing a method of fabricating a hydrogen catalyst layer according to some example embodiments of the present inventive concepts.

FIG. 9 is a SEM image showing preliminary layers of molybdenum disulfide (MoS₂) on horizontal and standing crystals of molybdenum dioxide (MoO₂) in accordance with Experimental Example 1.

FIG. 10 is a SEM image showing MoS₂ following removal of horizontal and standing crystals of molybdenum dioxide (MoO₂) in accordance with Experimental Example 1.

FIG. 11 is a graph showing Raman analysis results of a state in which preliminary layers of molybdenum disulfide (MoS₂) are formed on horizontal and standing crystals of molybdenum dioxide (MoO₂) in accordance with Experimental Example 1.

FIG. 12 is a graph showing Raman analysis results of a state in which horizontal and standing crystals of molybdenum dioxide (MoO₂) are removed in accordance with Experimental Example 1.

FIG. 13 illustrates a schematic diagram showing a process for hydrogen reduction using a device for hydrogen production according to some example embodiments of the present inventive concepts.

FIG. 14 is a graph showing hydrogen reduction efficiency for a device for hydrogen production according to some example embodiments of the present inventive concepts.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a perspective view of a device for hydrogen production according to some example embodiments of the present inventive concepts. FIG. 2A illustrates a cross-sectional view of a device for hydrogen production according to some example embodiments of the present inventive concepts. FIG. 2B illustrates an enlarged view showing section A of FIG. 2A.

Referring to FIGS. 1, 2A, and 2B, a device for hydrogen production according to some example embodiments of the present inventive concepts may include a substrate 100 and a hydrogen catalyst layer on the substrate 100. The hydrogen catalyst layer may include horizontal structures 210 and standing structures 220. The horizontal structures 210 and the standing structures 220 may be catalysts for reducing hydrogen ions (H⁺).

In certain embodiments, the substrate 100 may be a conductive substrate. The conductive substrate may include a metal or non-metal. The metal may be, for example, gold (Au). The non-metal may be, for example, graphene.

In other embodiments, the substrate 100 may be a dielectric substrate. The dielectric substrate may include a dielectric material. For example, the dielectric material may be silicon oxide (SiO_(x), 0<x<2).

The substrate 100 may be provided with the horizontal structures 210 and the standing structures 220. The horizontal structures 210 and the standing structures 220 may be irregularly arranged on the substrate 100. In some embodiments, the horizontal structures 210 and the standing structures 220 may be formed on the substrate 100.

The horizontal structure 210 may have a first thickness T1. The horizontal structure 210 may be shaped like a plate. For example, the first thickness T1 of the horizontal structure 210 may be less than a width of the horizontal structure 210. One or more horizontal structures 210 may extend in a direction parallel to a top surface 110 of the substrate 100.

The standing structure 220 may include a first standing segment 221, a second standing segment 222, and a first void VO1. The first and second standing segments 221 and 222 may be spaced apart from each other. The first void VO1 may be provided between the first and second standing segments 221 and 222. The first void VO1 may be a substantially hollow space.

One or more standing structures 220 may extend in a direction intersecting the top surface 110 of the substrate 100. For example, at least one of the standing structures 220 may extend in a direction perpendicular to the top surface 110 of the substrate 100. The first and second standing segments 221 and 222 of the standing structure 220 may also extend in a direction intersecting the top surface 110 of the substrate 100.

In some embodiments, two or more of the standing structures 220 may extend in a direction in which the two or more standing structures 220 would cross each other, if extended. For example, an extending direction of a first standing structure 220 may intersect an extending direction of a second standing structure 220. In this sense, the first standing structure 220 and the second standing structure 220 may not extend in parallel to each other.

The first and second standing segments 221 and 222 may each have a second thickness T2. Each of the first and second standing segments 221 and 222 may be shaped like a plate. Each of the first and second standing segments 221 and 222 may have a shape similar to that of the horizontal structure 210 when standing.

The first and second standing segments 221 and 222 may be parallel to each other. A first length L1 may be defined to refer to a shortest interval between the first and second standing segments 221 and 222. The first length L1 may be greater than the second thickness T2.

The first standing segment 221 may have a first inner sidewall 2211 facing the second standing segment 222. The second standing segment 222 may have a second inner sidewall 2221 facing the first standing segment 221. The first and second inner sidewalls 2211 and 2221 may be completely exposed to the first void VO1. The first void VO1 may be defined by the first and second inner sidewalls 2211 and 2221.

A second void VO2 may be provided between the standing structures 220. The second void VO2 may be a substantially hollow space.

The horizontal structures 210, the first standing segments 221, and/or the second standing segments 222 may include (or contain) molybdenum disulfide (MoS₂). The horizontal structures 210, the first standing segments 221, and/or the second standing segments 222 may include a monolayer or a multilayer (e.g., 2 or more layers) of molybdenum disulfide (MoS₂). The multilayer of MoS₂ may have a structure in which a plurality of monolayers of MoS₂ are stacked and connected by Van der Waals force(s).

In a device for hydrogen production according to some example embodiments of the present inventive concepts, because the first and second inner sidewalls 2211 and 2221 are exposed to the first void VO1, each of the first and second standing segments 221 and 222 may have a relatively large surface area. As a result, according to some example embodiments of the present inventive concepts, the device for hydrogen production may achieve relatively high efficiency in hydrogen reduction.

FIGS. 3A, 4A, 5A, and 6 illustrate schematic diagrams showing a method of fabricating a hydrogen catalyst layer according to some example embodiments of the present inventive concepts. FIGS. 3B, 4B, and 5B illustrate enlarged views showing section A of FIGS. 3A, 4A, and 5A, respectively.

Referring to FIGS. 3A and 3B, a substrate 100 may be disposed in a chamber 300. For example, the substrate 100 may be a conductive substrate. For another example, the substrate 100 may be a dielectric substrate. The chamber 300 may maintain a high vacuum state. For example, the chamber 300 may maintain a pressure below about 0.01 Torr.

An inert gas IG and a molybdenum oxide gas MOG may be supplied to the chamber 300 through an inlet 310 thereof. For example, the inert gas IG may include argon (Ar) and/or nitrogen (N). The molybdenum oxide gas MOG may include molybdenum oxide of a single species or a combination of molybdenum oxides of multiple species. The molybdenum oxide gas MOG may include molybdenum oxide having a chemical formula of Mo_(a)O_(b), wherein a and b may each independently be an integer equal to or greater than 1, and a ratio of b/a may be from 2 to 3. In some embodiments, the ratio of b/a may be between 2 and 3. For example, the molybdenum oxide gas MOG may be selected from the group consisting of MoO₂, MoO₃, Mo₂O₅, and a combination thereof However, the molybdenum oxide gas MOG may not include MoO₂ alone. When the molybdenum oxide gas MOG includes MoO₂ alone, the chamber 300 may be additionally supplied with one or both of MoO₃ and Mo₂O₅. In some embodiments, the molybdenum oxide gas MOG and/or chamber 300 comprises MoO₂ and MoO₃ and/or Mo₂O₅.

The inert gas IG may be supplied at a flow rate of about 200 sccm to about 500 sccm. When the chamber 300 is supplied with the inert gas IG and the molybdenum oxide gas MOG, a supply amount of the molybdenum oxide gas MOG may be controlled to maintain the chamber 300 at a pressure of about 1 Torr to about 1.2 Torr. Gases may be discharged through an outlet 320 from the chamber 300.

When the inert gas IG and the molybdenum oxide gas MOG are supplied, first horizontal crystals 410 and first standing crystals 420 may be formed on the substrate 100. For example, the formation of the first horizontal crystals 410 and the first standing crystals 420 may depend on a difference in temperature between the molybdenum oxide gas MOG and the substrate 100 and on a partial pressure of the molybdenum oxide gas MOG. The first horizontal crystals 410 and the first standing crystals 420 may include molybdenum oxide of a single species or a combination of molybdenum oxides of multiple species. The first horizontal crystals 410 and the first standing crystals 420 may each include molybdenum oxide having a chemical formula of Mo_(c)O_(d), wherein c and d may each independently be an integer equal to or greater than 1, and a ratio of d/c may be from 2 to 3. In some embodiments, the ratio of d/c may be between 2 and 3. For example, the molybdenum oxide gas MOG may be selected from the group consisting of MoO₂, MoO₃, Mo₂O₅, and a combination thereof. However, the molybdenum oxide gas MOG may not include MoO₂ alone. When the molybdenum oxide gas MOG includes MoO₂ alone, the chamber 300 may be additionally supplied with one or both of MoO₃ and Mo₂O₅. In some embodiments, the molybdenum oxide gas MOG and/or chamber 300 comprises MoO₂ and MoO₃ and/or Mo₂O₅.

The first horizontal crystals 410 and the first standing crystals 420 may be irregularly arranged on the substrate 100. The first horizontal crystals 410 and the first standing crystals 420 may each have a plate shape. The first horizontal crystals 410 may extend in a direction parallel to a top surface 110 of the substrate 100. The first standing crystals 420 may extend in a direction intersecting the top surface 110 of the substrate 100.

Referring to FIGS. 4A and 4B, heating may be performed to increase a temperature of the substrate 100. A temperature rising rate of the substrate 100 may fall in a range of about 50° C./min to about 55° C./min. When the temperature rising rate of the substrate 100 is set at about 50° C./min to about 55° C./min, the first horizontal crystals 410 and the first standing crystals 420 may be prevented from their loss due to sublimation. In some embodiments, the temperature rising rate of the substrate 100 is set between about 50° C./min and about 55° C./min.

When the temperature of the substrate 100 reaches about 650° C. to about 780° C., a sulfur gas SG may be supplied through the inlet 310 to the chamber 300. The sulfur gas SG may be supplied at a flow rate above about 50 sccm.

When the sulfur gas SG is supplied, the first horizontal crystals 410 and the first standing crystals 420 may react with the sulfur gas SG. When the first horizontal crystals 410 and the first standing crystals 420 react with the sulfur gas SG, oxygen (O) atoms in the first horizontal crystals 410 and/or the first standing crystals 420 may be at least partially reduced. The reduction of oxygen (O) may convert the first horizontal crystals 410 into second horizontal crystals 510 and also convert the first standing crystals 420 into second standing crystals 520.

The second horizontal crystals 510 and the second standing crystals 520 may include molybdenum dioxide (MoO₂). The molybdenum dioxide (MoO₂) in the second horizontal crystals 510 and the second standing crystals 520 may be formed when oxygen (O) is at least partially reduced from molybdenum oxide having a chemical formula of Mo_(c)O_(d). The second horizontal crystals 510 and the second standing crystals 520 may each be shaped like a plate. The second horizontal crystal 510 may have a third thickness T3. The third thickness T3 may be, on average, less than a thickness T3′ of the first horizontal crystal 410. The second standing crystal 520 may have a fourth thickness T4. The fourth thickness T4 may be, on average, less than a thickness T4′ of the first standing crystal 420. The second horizontal crystals 510 may extend in the direction parallel to the top surface 110 of the substrate 100. The second standing crystals 520 may extend in the direction intersecting the top surface 110 of the substrate 100.

Each of the second horizontal crystals 510 may include a first surface 511 perpendicular to a direction along the third thickness T3 and also include second surfaces 512 parallel to the direction along the third thickness T3. Each of the second standing crystals 520 may include third surfaces 521 perpendicular to a direction along the fourth thickness T4 and also include fourth surfaces 522 parallel to the direction along the fourth thickness T4.

Referring to FIGS. 5A and 5B, the temperature of the substrate 100 may be increased. While the temperature of the substrate 100 is increased, the sulfur gas SG may be continuously supplied. The temperature of the substrate 100 may be increased up to a maximum temperature of about 900° C. to about 1100° C. The maximum temperature of the substrate 100 may be kept for about 10 minutes or more.

When the temperature of the substrate 100 reaches the maximum temperature, the sulfur gas SG may react with the second horizontal crystals 510 and the second standing crystals 520. When the second horizontal crystals 510 and the second standing crystals 520 react with the sulfur gas SG, a preliminary layer 600 may be formed on the second horizontal crystals 510 and the second standing crystals 520. The preliminary layer 600 may be conformally formed on the first and second surfaces 511 and 512 of the second horizontal crystals 510 and on the third and fourth surfaces 521 and 522 of the second standing crystals 520. In some embodiments, the preliminary layer 600 is conformally formed on exposed surfaces (e.g., surfaces exposed to and/or contacted with the sulfur gas SG) of the second horizontal crystals 510 and the second standing crystals 520.

The preliminary layer 600 may include molybdenum disulfide (MoS₂). The preliminary layer 600 may be a monolayer of molybdenum disulfide (MoS₂) or a multilayer of molybdenum disulfide (MoS₂). The multilayer may have a structure in which a plurality of monolayers are stacked and connected by Van der Waals force(s). The longer the time in which the maximum temperature of the substrate 100 is maintained, the greater the number of stacked molecular layers of the preliminary layer 600.

The preliminary layer 600 may include first segments 610 formed on the second surfaces 512 of the second horizontal crystals 510 and also include second segments 620 formed on the fourth surfaces 522 of the second standing crystals 520. The second segment 620 on the second standing crystal 520 may have a second length L2 in the direction along the fourth thickness T4 of the second standing crystal 520.

Referring to FIG. 6, an etchant EC may be used to remove the second horizontal crystals 510 and the second standing crystals 520. The etchant EC may include a material capable of etching molybdenum dioxide (MoO₂). For example, the etchant EC may include a buffered oxide etchant (BOE) and/or hydrofluoric acid (HF).

When the etchant EC is sprayed onto the substrate 100, the etchant EC may pass through the preliminary layer 600 to remove the second horizontal crystals 510 and the second standing crystals 520 within the preliminary layer 600.

Referring back to FIGS. 1, 2A, and 2B, when the second horizontal crystals 510 are removed, the first segments 610 of the preliminary layer 600 may also be removed from the second surfaces 512 of the second horizontal crystals 510. When the second standing crystals 520 are removed, the second segments 620 of the preliminary layer 600 may also be removed from the fourth surfaces 522 of the second standing crystals 520.

The preliminary layer 600 may be formed and/or transformed into horizontal structures 210 and standing structures 220. The horizontal structure 210 may be on and/or attached to the top surface 110 of the substrate 100 because of the removal of the second horizontal crystals 510 and the first segments 610 of the preliminary layer 600. A first void VO1 may be formed between a first standing segment 221 and a second standing segment 222 of the standing structure 220 because of the removal of the second standing crystals 520 and the second segments 620 of the preliminary layer 600. The formation of the first void VO1 may expose a first inner sidewall 2211 of the first standing segment 221 and also expose a second inner sidewall 2221 of the second standing segment 222.

FIGS. 7 and 8 illustrate schematic diagrams showing a method of fabricating a hydrogen catalyst layer according to some example embodiments of the present inventive concepts. Except for that discussed below, a method of fabricating a hydrogen catalyst layer according to some example embodiments of the present inventive concepts is similar to that according to the embodiment discussed above with reference to FIGS. 3A, 4A, and 5A.

Referring to FIG. 7, the inert gas IG may be supplied through the inlet 310 to the chamber 300.

A molybdenum oxide powder MOP may be in and/or provided in the chamber 300. The molybdenum oxide powder MOP may include molybdenum oxide of a single species or a combination of molybdenum oxides of multiple species. The molybdenum oxide powder MOP may include molybdenum oxide having a chemical formula of Mo_(a)O_(b), wherein a and b may each independently be an integer equal to or greater than 1, and a ratio of b/a may be from 2 to 3. In some embodiments, the ratio of b/a may be between 2 and 3. For example, the molybdenum oxide powder MOP may be selected from the group consisting of MoO₂, MoO₃, Mo₂O₅, and a combination thereof. However, in some embodiments, the molybdenum oxide powder MOP may not include MoO₂ alone. When the molybdenum oxide powder MOP includes only MoO₂ as the molybdenum oxide species, the chamber 300 may additionally be supplied with one or both of MoO₃ and Mo₂O₅. In some embodiments, the molybdenum oxide powder MOP and/or chamber 300 comprises MoO₂ and MoO₃ and/or Mo₂O₅.

The molybdenum oxide powder MOP may be vaporized due to an increase in temperature of the chamber 300. As the molybdenum oxide powder MOP is vaporized, the chamber 300 may be supplied with gaseous molybdenum oxide such as MoO_(n), wherein n is less than or equal to 3.

Referring to FIG. 8, a sulfur powder SP may be in and/or provided in the chamber 300. The sulfur powder SP may be vaporized due to an increase in temperature of the chamber 300. As the sulfur powder SP is vaporized, the chamber 300 may be supplied with gaseous sulfur (S).

The following will describe an experimental example utilizing a device for hydrogen reduction according to some example embodiments of the present inventive concepts.

EXPERIMENTAL EXAMPLE 1

A graphene substrate was loaded in a chamber maintained at a pressure of 0.01 Torr. The chamber was supplied with nitrogen (N) gas at a flow rate of 500 sccm. A molybdenum trioxide (MoO₃) gas was supplied to the chamber, the chamber was maintained at a pressure of 1 Torr, and horizontal and standing crystals of molybdenum trioxide (MoO₃) were formed.

A temperature of the substrate was increased at a rate of 50° C./min. A sulfur (S) powder was vaporized in the chamber. As the sulfur (S) powder was vaporized, a sulfur (S) gas reacted with the horizontal and standing crystals of molybdenum trioxide (MoO₃). Horizontal and standing crystals of molybdenum dioxide (MoO₂) were formed by the reaction of the sulfur (S) gas with the horizontal and standing crystals of molybdenum trioxide (MoO₃).

The temperature of the substrate was increased to 1000° C. The substrate was maintained at a temperature of 1000° C. for 10 minutes. The sulfur (S) gas and the horizontal and standing crystals of molybdenum dioxide (MoO₂) were reacted to form a preliminary layer containing molybdenum disulfide (MoS₂) on the horizontal and standing crystals of molybdenum dioxide (MoO₂).

A buffered oxide etchant (BOE) was used to remove the horizontal and standing crystals of molybdenum dioxide (MoO₂).

FIG. 9 illustrates a SEM image showing molybdenum disulfide (MoS₂) preliminary layers formed on horizontal and standing crystals of molybdenum dioxide (MoO₂) in accordance with Experimental Example 1. FIG. 10 illustrates a SEM image showing a state in which horizontal and standing crystals of molybdenum dioxide (MoO₂) have been removed in accordance with Experimental Example 1.

FIG. 9 may show the preliminary layers of molybdenum disulfide (MoS₂) covering the horizontal and standing crystals of molybdenum dioxide (MoO₂), and FIG. 10 may show horizontal structures and standing segments of molybdenum disulfide (MoS₂). Comparing FIG. 9 and FIG. 10, it may be ascertained that each second length (see L2 of FIG. 5B) of second segments (see 620 of FIG. 5B) in the preliminary layers of molybdenum disulfide (MoS₂) is relatively greater than each second thickness (see T2 of FIG. 2B) of the standing segments (see 221 and 222 of FIG. 2B).

FIG. 11 illustrates a graph showing Raman analysis results of a state in which the preliminary layers of molybdenum disulfide (MoS₂) are formed on the horizontal and standing crystals of molybdenum dioxide (MoO₂) in accordance with Experimental Example 1. FIG. 12 illustrates a graph showing Raman analysis results of a state in which the horizontal and standing crystals of molybdenum dioxide (MoO₂) have been removed in accordance with Experimental Example 1.

Referring to FIG. 11, Raman analysis may confirm the presence of molybdenum dioxide (MoO₂) and molybdenum disulfide (MoS₂).

Referring to FIG. 12, Raman analysis may confirm the absence of molybdenum dioxide (MoO₂) and the presence of molybdenum disulfide (MoS₂).

FIG. 13 illustrates a schematic diagram showing a process for hydrogen reduction using a device for hydrogen production according to some example embodiments of the present inventive concepts.

Referring to FIG. 13, a solution 720 may be provided and/or prepared in a vessel 710. The solution 720 may include a hydrogen ion (H⁺). For example, the solution 720 may include water (H₂O) and/or sulfuric acid (H₂SO₄). When the substrate 100, on which the horizontal structures 210 and the standing structures 220 are provided, is immersed in the solution 720 and supplied with a voltage, the hydrogen ion (H⁺) in the solution 720 may be reduced by the horizontal structures 210 and the standing structures 220. A current resulting from the reduction of the hydrogen ion (H⁺) may be measured to obtain hydrogen reduction efficiency of a device for hydrogen production.

FIG. 14 illustrates a graph showing hydrogen reduction efficiency of a device for hydrogen production according to some example embodiments of the present inventive concepts.

FIG. 14 may show how hydrogen reduction efficiency depends on the kind of catalyst. In FIG. 14, the expression of “Au” may indicate an experimental result of hydrogen reduction catalyzed by gold (Au), the expression of “Lateral MoS₂” may indicate an experimental result of hydrogen reduction catalyzed by molybdenum disulfide (MoS₂) horizontally grown on a substrate, the expression of “Vertical MoO₂/MoS₂” may indicate an experimental result of hydrogen reduction catalyzed by horizontal and standing crystals of molybdenum dioxide (MoO₂) and preliminary layers of molybdenum disulfide (MoS₂) that are formed in accordance with Experimental Example 1, and the expression of “Vertical MoS₂” may indicate an experimental result of hydrogen reduction catalyzed by molybdenum disulfide (MoS₂) from which horizontal and standing crystals of molybdenum dioxide (MoO₂) are removed in accordance with Experimental Example 1.

When a substrate and catalysts are provided into a solution of 0.5 M sulfuric acid, and when a hydrogen reduction current (J) is measured while the substrate is supplied with a voltage (V), it may be confirmed that the result expressed by Vertical MoS₂ has the highest efficiency of hydrogen reduction.

According to some example embodiments of the present inventive concepts, a device for hydrogen production may be configured to allow molybdenum disulfide to have a relatively large surface area to achieve high efficiency of hydrogen reduction.

Although some example embodiments of the present inventive concepts have been discussed with reference to accompanying figures, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the present inventive concepts. It therefore will be understood that the some example embodiments described above are just illustrative but not limitative in all aspects. 

What is claimed is:
 1. A method of fabricating a hydrogen catalyst layer, the method comprising: providing a substrate comprising a first horizontal crystal and a first standing crystal that each include molybdenum oxide; forming a second horizontal crystal, a second standing crystal, and a preliminary layer on the second horizontal and second standing crystals by supplying a sulfur gas onto the first horizontal crystal and the first standing crystal, the preliminary layer including molybdenum disulfide (MoS₂); and removing the second horizontal crystal and the second standing crystal.
 2. The method of claim 1, wherein forming the second horizontal crystal and the second standing crystal includes reducing at least a portion of oxygen atoms in the first horizontal crystal and in the first standing crystal.
 3. The method of claim 1, wherein the second horizontal crystal and the second standing crystal include molybdenum dioxide (MoO₂).
 4. The method of claim 1, wherein the molybdenum oxide in the first horizontal crystal and the first standing crystal has a chemical formula of Mo_(a)O_(b), wherein a and b are each independently an integer equal to or greater than 1, and a ratio of b/a is from 2 to
 3. 5. The method of claim 1, wherein providing the substrate comprising the first horizontal crystal and the first standing crystal includes supplying the substrate with an inert gas and a molybdenum oxide gas.
 6. The method of claim 1, wherein removing the second horizontal crystal and the second standing crystal includes spraying the substrate with an etchant that etches the second horizontal crystal and the second standing crystal.
 7. The method of claim 1, wherein forming the second horizontal crystal and the second standing crystal includes increasing a temperature of the substrate.
 8. A method of fabricating a hydrogen catalyst layer, the method comprising: forming on a substrate a first horizontal crystal and a first standing crystal that each include molybdenum dioxide (MoO₂); forming a preliminary layer on the first horizontal crystal and the first standing crystal; and removing the first horizontal crystal and the first standing crystal, wherein the preliminary layer includes molybdenum disulfide (MoS₂).
 9. The method of claim 8, wherein the first horizontal crystal extends in a first direction that is parallel to a top surface of the substrate, and the first standing crystal extends in a second direction that intersects the top surface of the substrate.
 10. The method of claim 8, wherein forming the preliminary layer on the first horizontal crystal and the first standing crystal includes supplying a sulfur gas onto the substrate.
 11. The method of claim 8, wherein forming on the substrate the first horizontal crystal and the first standing crystal includes: forming on the substrate a second horizontal crystal and a second standing crystal; and reducing at least a portion of oxygen atoms in the second horizontal crystal and in the second standing crystal.
 12. The method of claim 8, wherein removing the first horizontal crystal and the first standing crystal includes spraying the substrate with an etchant that etches the first horizontal crystal and the first standing crystal.
 13. The method of claim 8, wherein removing the first horizontal crystal and the first standing crystal includes forming a standing structure, wherein the standing structure includes: a first standing segment that extends in a direction intersecting a top surface of the substrate; a second standing segment that extends in the direction intersecting the top surface of the substrate; and a first void between the first standing segment and the second standing segment.
 14. The method of claim 13, wherein the first standing segment and the second standing segment are parallel to each other.
 15. A device for hydrogen production, the device comprising: a substrate; a horizontal structure that lies on the substrate and extends in a first direction that is parallel to a top surface of the substrate; and a first standing structure and a second standing structure that each extend in a direction that intersects the top surface of the substrate, wherein each of the first and second standing structures includes: a first standing segment and a second standing segment that are parallel to each other; and a first void between the first standing segment and the second standing segment, wherein extending directions of the first and second standing structures cross each other.
 16. The device of claim 15, wherein the horizontal structure, the first standing segment, and the second standing segment each include molybdenum disulfide (MoS₂).
 17. The device of claim 15, wherein a thickness of each of the first and second standing segments is less than a shortest interval between the first standing segment and the second standing segment.
 18. The device of claim 15, wherein the first standing segment includes a first inner sidewall facing the second standing segment, the second standing segment includes a second inner sidewall facing the first standing segment, and the first void completely exposes the first and second inner sidewalls.
 19. The device of claim 15, wherein the horizontal structure, the first standing segment, and the second standing segment each have a plate shape.
 20. The device of claim 15, wherein a second void is provided between the first standing structure and the second standing structure. 